[Not Applicable]
1. Field of the Invention
The present invention relates to an apparatus and method for forming a golf ball cover layer. More specifically, the present invention relates to an apparatus and method for forming a thermoset polyurethane cover on a golf ball core.
2. Description of the Related Art
Golf balls may comprise one-piece constructions or they may include several layers including a core, one or more intermediate layers and an outer cover that surrounds any intermediate layer and the core. In multi-component golf balls, there exists an inner core. Often, this core is made by winding a band of elastomeric material about a spherical elastomeric or liquid-filled center. Alternatively, the core may be a unitary spherical core made of a suitable solid elastomeric material. One such material that is conventionally used for the core of golf balls is a base rubber, such as polybutadiene, which is cross-linked with a metal acrylate, such as zinc diacrylate.
In the construction of some multi-component golf balls, an intermediate boundary layer is provided outside and surrounding the core. This intermediate boundary layer is thus disposed between the core and the outer cover of the golf ball.
Located outwardly of the core and any intermediate boundary layer is a cover. The cover is typically made from any number of thermoplastic or thermosetting materials, including thermoplastic resins such as ionomeric, polyester, polyetherester or polyetheramide resins; thermoplastic or thermoset polyurethanes; natural or synthetic rubbers such as balata (natural or synthetic) or polybutadiene; or some combination of the above.
Golf balls are typically manufactured by various molding processes, whether one-component or multicomponent balls. Generally, the core of the golf ball is formed by casting, compression molding, injection molding or the like. If an intermediate boundary layer is desired, one or more intermediate boundary layers are added over the core by any number of molding operations, including casting, compression molding, and/or injection molding. The cover is then formed over the core and intermediate boundary layers, if present, through casting, compression molding, and/or injection molding.
One example of a conventional golf ball manufacturing process is described in U.S. Pat. No. 3,068,522, issued on Dec. 18, 1962 (the xe2x80x3522 patent). The manufacturing process disclosed in the xe2x80x3522 patent uses a molding press having upper and lower die portions that surround a golf ball core. A retractable seat contacts the golf ball core to place the same in the desired orientation within the die cavity. The cover material is then injected into the die cavity to form the cover of the ball. The xe2x80x3522 patent further discloses that the timing of the retraction of the retractable seat is critical and depends, in part, on the flow rate of the cover material into the mold cavity. In order to prevent the retardation of the flow rate or pre-hardening of the injected coating material, the xe2x80x3522 patent teaches that in some instances, it may be necessary to heat the molding dies and pre-heat the golf ball core to a temperature slightly above ambient temperature.
Another example, U.S. Pat. No. 5,194,191 (the xe2x80x3191 patent), issued Mar. 16, 1993 discloses a method of preparing thread-wound golf balls. In the xe2x80x3191 patent, a rubber thread or material is wound around a frozen core of material to form a core. Immediately thereafter, the core undergoes microwave heating to rapidly thaw the frozen core without heating the rubber thread layer and without moisture condensation taking place on the surface of the core. The method of the xe2x80x3191 patent allegedly reduces the core thawing time and eliminates the need for a drying step.
These and other current golf ball manufacturing processes continue to suffer from a number of disadvantages. For example, when the outer cover of the golf ball is made from a thermoset material, e.g., thermoset polyurethane, the core and any intermediate boundary layer(s) tend to undergo thermal expansion during the casting of the outer cover, as heat is generated by the exothermic reaction of the thermoset processes used in the formation of the cover. As the cover forms, and before the cover develops sufficient green strength, the thermal expansion of the core and any intermediate boundary layer, in turn, may cause the outer cover of the golf ball to fracture or crack. Although this problem is particularly relevant to covers that are formed of thermoset polyurethane, it is not believed to be limited thereto. Similar problems may arise with other materials and processes.
Cracking is not the only problem with the current conventional methods of manufacturing golf balls. Since a temperature gradient exists between the core, intermediate layer, if any, and the outer cover, the central portion of the ball acts as a heat sink that absorbs heat given off during the cover-making process. In this regard, the reaction that takes place to cure the outer cover takes longer given the cooler temperature in the inner core of the ball. Production cycle times are thus adversely increased.
Consequently, there remains a need for methods of manufacturing golf balls that do not suffer from the above disadvantages. Moreover, a system and method that permits precision centering of a core in relation to a cover is greatly desired.
The present invention provides a method and system for automatically casting a thermoset layer over a golf ball precursor product, such as a core with a boundary layer. The present invention allows for a plurality of golf ball precursor products to be simultaneously cast molded within a plurality of cavities containing the thermoset material. A preferred thermoset material is a thermoset polyurethane material.
One aspect of the present invention is a method for casting a thermoset layer on each of a plurality of golf ball precursor products. The method includes dispensing a flowable material from a stationary dispenser into each of a plurality of cavities disposed on a first mold half and a second mold half. The flowable material is a thermoset polymer material, precursor thermoset polymer materials, or a mixture thereof. Next, each of the plurality of golf ball precursor products is inserted into a corresponding cavity of the plurality of cavities of the first mold half.
Next, the first mold half is inverted and mated with the second mold half to form a mold assembly to enclose each of the plurality of golf ball precursor products within a spherical cavity to form a thermoset layer on each of the plurality of golf ball precursor products. Next, the mold assembly is heated to cure the thermoset layer on each of the golf ball precursor products. After curing, the mold assembly is separated into the first mold half and the second mold half to expose each the plurality of golf ball precursor products with a thermoset layer thereon for removal from the second mold half.
Another aspect of the present invention is a system for casting a thermoset layer on a golf ball precursor product. The system includes a mold assembly having first and second mold halves with each having a plurality of hemispherical cavities therein. The system also includes a dispensing mechanism having a stationary dispenser and an X-Y gantry. The stationary dispenser dispenses a flowable material into each of the plurality of cavities while the X-Y gantry moves each of the mold halves in a figure eight pattern below it. The system also includes an insertion mechanism having a plurality of vacuum cups for suctioning a plurality of golf ball precursor products from a platen and moving downward along a longitudinal pathway. The insertion mechanism also has a lifter for lifting the first mold half upward along the longitudinal pathway toward the vacuum cups. The system also includes a mold assembly mechanism for inverting the first mold half and mating it with the second mold half. The system also includes a conveyor for transferring the mold assembly along the system, and a heating oven for curing a thermoset layer on each of the golf ball precursor products. Finally, the system includes a de-molding mechanism for separating the first mold half from the second mold half, and removing each of the thermoset layered golf balls from the first mold half.
Having briefly described the present invention, the above and further objects, features and advantages thereof will be recognized by those skilled in the pertinent art from the following detailed description of the invention when taken in conjunction with the accompanying drawings.